Applied Composite Materials (v.16, #2)

The surfaces of carbon-carbon (C/C) aircraft brakes are usually coated with anti-oxidant to protect them from oxidation. These surfaces do not include the friction surfaces since it is known that when anti-oxidant get onto the friction surface, the friction coefficient decreases. The anti-oxidant migration (AOM), however, happens during processing, heat treatment and application. In this study, phosphorus based anti-oxidants inhibited 3-D C/C aircraft brake system was investigated. The effects of their migration on friction and wear in the 3-D C/C brakes were revealed by sub-scale dynamometer tests and microscopic analysis. Dynamometer results showed that when AOM occurred, both landing and taxi coefficients decreased in humid environment and the wear was slightly lowered. Microscopic study showed that under high humidity conditions there was no formation of the friction film.
Keywords: Anti-oxidant; Friction; Wear; Migration; Carbon; Composite

Oxidation Behavior of C/SiC Composite with CVD SiC-B4C Coating in a Wet Oxygen Environment by Wenbin Yang; Litong Zhang; Laifei Cheng; Yongsheng Liu; Laifei Cheng; Weihua Zhang (83-92).
A two-layered self healing coating with a B4C internal layer and a SiC external layer is prepared on C/SiC composite by chemical vapor deposition (CVD). Microstructure and component of the coating was analyzed by SEM, EDS, and XRD. Oxidation behavior of SiC-B4C coated C/SiC composite was compared with SiC-SiC coated C/SiC in an environment of $${{P_{{ ext{H}}_{ ext{2}} { ext{O}}} } mathord{left/ {vphantom {{P_{{ ext{H}}_{ ext{2}} { ext{O}}} } {{{P_{{ ext{O}}_{ ext{2}} } } mathord{left/ {vphantom {{P_{{ ext{O}}_{ ext{2}} } } {P_{{ ext{Ar}}} }}} ight. kern- ulldelimiterspace} {P_{{ ext{Ar}}} }}}}} ight. kern- ulldelimiterspace} {{{P_{{ ext{O}}_{ ext{2}} } } mathord{left/ {vphantom {{P_{{ ext{O}}_{ ext{2}} } } {P_{{ ext{Ar}}} }}} ight. kern- ulldelimiterspace} {P_{{ ext{Ar}}} }}}} = {{14} mathord{left/ {vphantom {{14} {{8 mathord{left/ {vphantom {8 {78}}} ight. kern- ulldelimiterspace} {78}}}}} ight. kern- ulldelimiterspace} {{8 mathord{left/ {vphantom {8 {78}}} ight. kern- ulldelimiterspace} {78}}}}$$ at 700°C, 1,000°C and 1,200°C for 100 h, respectively. It is demonstrated that the SiC-B4C coating is more efficient to protect the composite from oxidation than SiC-SiC coating below 1,000°C due to the self healing behavior. After oxidized at 700°C for 100 h, the residual flexural strength of SiC-B4C coated C/SiC is about 86%, and that of SiC-SiC coated is about 64%. While after oxidized at 1,200°C, the former is about 86% and the later is about 89%. This is due to the enhanced evaporation of B2O3 at higher temperature.
Keywords: Oxidation behavior; Self healing; Coating; Chemical vapor deposition; Boron carbide; Residual strength

Jute fibre reinforced polyester composites were developed and characterized for friction and sliding wear properties. Effect of fibre orientation and applied load on tribological behaviour of jute fibre reinforced polyester composites were determined. It is found that wear resistance was maximum in TT sample, where fibres were normal to sliding direction. Wear rate under sliding mode follows this trend; WTT < WLT LL LL sample showed higher capability to sustain the load whereas lowest wear resistance found in this case. The coefficient of friction found highest for TT sample and lowest for LT sample. The coefficient of friction decreased with increase of applied load. Worn surfaces were analysed and discussed with the help of SEM.
Keywords: Jute fibre; Polyester; Orientation; Friction; Sliding wear

Based on the two-dimensional resin flow and fiber compaction model developed by our group, we studied the cured laminate thickness uniformity of the L-shaped CF/BMI resin laminates and the effects of lay-up type and structural elements on it. Both the simulated and experimental data showed that the quasi-isotropic laminate thickness was more uniform than that of the [90°]n laminates and the cured thickness of laminates molded by rigid convex tool was more uniform than that molded by the rigid concave tool. Lay-up type has a great influence on the cured laminate thickness uniformity. For the quasi-isotropic laminates, the structural elements, such as curvature radius, flat part length, and the number of plies, did not have much influence on the cured laminate thickness uniformity in the studied scope. For the [90°]n laminates, the corner radius has a larger effect on the corner consolidation in comparison with the flat part length and the number of plies. According to the simulated results, resin pressure and consolidation time were largely affected by the lay-up type, due to the different permeability and compressibility. The rich resin defect was observed in the metallographic photos of the corner region of the [90°]n laminates fabricated with the rigid concave tool, which demonstrated that the resin flow in the laminates played an important rule and validated the numerical prediction. Good agreement between the simulated results and experimental data demonstrated the reliability and universality of the numerical simulation method. These results are greatly helpful for the control of defects in angle-bended laminates and the optimization of cure cycle in autoclave process.
Keywords: Autoclave; Simulation; L-shaped laminates; Resin flow; Defects

Direct Forming of All-Polypropylene Composites Products from Fabrics made of Co-Extruded Tapes by B. Alcock; N. O. Cabrera; N. M. Barkoula; T. Peijs (117-134).
Many technologies presented in literature for the forming of self-reinforced or all-polymer composites are based on manufacturing processes involving thermoforming of pre-consolidated sheets. This paper describes novel direct forming routes to manufacture simple geometries of self-reinforced, all-polypropylene (all-PP) composites, by moulding fabrics of woven co-extruded polypropylene tapes directly into composite products, without the need for pre-consolidated sheet. High strength co-extruded PP tapes have potential processing advantages over mono-extruded fibres or tapes as they allow for a larger temperature processing window for consolidation. This enlarged temperature processing window makes direct forming routes feasible, without the need for an intermediate pre-consolidated sheet product. Thermoforming studies show that direct forming is an interesting alternative to stamping of pre-consolidated sheets, as it eliminates an expensive belt-pressing step which is normally needed for the manufacturing of semi-finished sheets products. Moreover, results from forming studies shows that only half the energy was required to directly form a simple dome geometry from a stack of fabrics compared to stamping the same shape from a pre-consolidated sheet.
Keywords: Self reinforced composites; Thermoforming; Thermoplastic composites; Fabrics/textiles